Currently an image scanner having a line scan image sensor also known as a linear sensor are used for input scanning of images of sheet-like reflective originals or documents. In this type of scanner, a linear image sensor moves along a path relative to the original and scans a line at a time. This type of scanner has the advantage that the volume of the total apparatus can be reduced because the optical system for transmitting images onto the sensor does not occupy a large space. Where transparent film is used, however, it is necessary to use an optical system which is different from the previously mentioned one utilized for reflective originals.